S/390: z13 inline stpcpy implementation.

S/390: z13 inline stpcpy implementation.

A handwritten loop for stpcpy using the new z13 vector instructions
appears to be much faster than the millicoded instruction.  However,
the implementation is much longer and therefore will only be enabled
when optimization for speed.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/md/movstr-2.c: New test.

gcc/ChangeLog:

	* config/s390/s390-protos.h: Add s390_expand_vec_movstr prototype.
	* config/s390/s390.c (s390_expand_vec_movstr): New function.
	* config/s390/s390.md ("movstr<P:mode>"): Call
	s390_expand_vec_movstr.

From-SVN: r233550